A trocar assembly is a surgical instrument typically comprised of a trocar obturator having a puncturing distal end and a trocar sheath or cannula which is adapted to slide over the outer diameter of the trocar obturator. The trocar obturator and cannula are used together to puncture tissue to gain access to a surgical site. Once the puncture is made the trocar obturator is adapted to be removed from the cannula thus permitting the use of operating instruments through the hollow cannula tube.
The distal end of most trocar obturators forms a sharp tip. Most available trocars have a safety shielded tip. The safety shield of these trocars generally slides proximal and distal to expose and cover the sharp tip. The safety shield will cover the tip until a force has been applied to the shield such as when the trocar assembly is being inserted through an abdominal wall. Typically, in the case of these safety shielded obturators, after the tip has pierced the abdominal wall the force is released from the shield allowing it to move distally to cover the tip in a locked position.
Other trocars have been used in which the tip moves distally and proximally in and out of the trocar cannula. The obturator tip may or may not have, in addition, a safety shield which covers the tip when the obturator is removed from the cannula. These safety shields, however do not cover the tip when the obturator is inserted in the cannula. A disadvantage of these retracting obturator trocar assemblies is the tip which remains flush within the distal end of the cannula when it is in the fully retracted position, is nonetheless exposed by the opening on the distal end of the cannula. Another disadvantage of these devices is the inability of the user to use the tip which has retracted, to reenter the abdomen through the existing puncture site. This procedure is commonly done with existing safety shield retracting trocars by locking the shield forward without first rearming the trocar and thus without exposing the sharp tip. Since the retraction mechanism in a retracting trocar obturator depends on a resistive force against the blade to trigger the blade retraction, reentry through an existing opening in the abdomen produces little resistive force against the blade raising the possibility-that the blade will not retract properly. Other known retractable trocar obturators do not provide a protective end for users when the obturator is outside of the cannula. Also, known retractable trocar obturators have bulky handles in which the retracting mechanism is typically located. This makes the trocar difficult and awkward to handle.